1. Introduction Montelupo Fiorentino is a little town about 20 km west of Florence, characterised by the presence of a large number of ceramic and glass factories. Since the PM 10 mean value in the area is higher than the new Air Quality Directive (1999/39/EC) recommended value and potentially harmful elements can be emitted by the local industrial activities, we decided to start a deep investigation to determine the mass concentrations and the elemental composition of the PM 10, PM 2.5 and PM 1 fractions of the aerosol. Sampling PM 10, PM 2.5 and PM 1 samples were collected, on a daily basis, on 47 mm diameter Teflon filters, by three single-mode sequential samplers (one PARTISOL 2025 and two IND PNS15D), located 4 m above ground level, on the roof of an air quality monitoring station. Mass concentrations were obtained using an analytical balance. The sampling campaign lasted from the 24 th of September 2002 to the 2 nd of July 2003: during certain periods we mounted the same inlet on all the instruments to carry on a systematic comparison between the three devices (about ten days for each fraction); during 3 weeks we put a different inlet on each instrument to measure the granulometric fraction ratios (i.e. PM 2.5 /PM 10 and PM 1 /PM 10 ). Starting from the 21 st of December we continued the sampling with only one IND sampler with PM 10 inlet. Particulate matter composition in an industrial district near to Florence Massimo Chiari a, Piero Del Carmine a, Franco Lucarelli a, Graziella Marcazzan b, Silvia Nava c, Leonardo Paperetti a, Paolo Prati c, Gianluigi Valli b, Roberta Vecchi b, Alessandro Zucchiatti c a Physic Dept. and INFN - Firenze, b Istituto di Fisica Generale Applicata - Milano, c Physic Dept. and INFN - Genova 10 cm surface-barrier detectors:  = 150°  C, N, O;  = 30°  H proton beam: 3 MeV, 5 nA (3  C per sample ) aerosol sample Faraday cup HPGe detector Percentage contributions of the eight most abundant elements detected by PIXE and PESA to the total gravimetric mass. ‘Other PIXE’ is the sum of the other elements detected by PIXE. The values are averaged over the 3 weeks of simultaneous sampling of the three fractions. Ion Beam Analysis at the Van de Graaff accelerator in Florence The concentrations of the elements with Z > 10 were measured by Particle Induced X-ray Emission (PIXE) at the external beam facility. PIXE measurements were performed at 2.2 MeV proton energy to reduce the Compton  -ray background produced by the fluorine in the Teflon filters. The X-ray spectra have been fitted for 28 elements (Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, Sr, Zr, Pb, Mo, Cd, Sb, Sn) using the GUPIX software package. To obtain a complete reconstruction of the aerosol mass, we implemented the detection of H, C, N and O by in-vacuum Particle Elastic Scattering Analysis (PESA). Assuming a constant C/F ratio in Teflon, the contribution due to the carbon content of the filter to be subtracted to the total C signal is proportional to the ‘local’ filter thickness and to its F content, which can be measured by Particle Induced  -ray Emission (PIGE) analysis (simultaneously with PESA) exploiting the 19 F(p,p’  ) 19 F reaction (E  = 110 keV). Q uantitative results were obtained by direct comparison with thin standards (supplied by Micromatter Inc.) for PIXE and with a thin Upilex-S foil (H 10 C 22 N 2 O 4 ) for PESA. Typical MDLs were 0.1  g/m 3 for H, 1  g/m 3 for C, 0.5  g/m 3 for both N and O, and 1-10 ng/m 3 for all the other elements. The absolute concentration of all the elements could be measured with an error ranging from ±5% to ±30% with the bigger errors affecting concentration values approaching MDLs. 10 cm proton beam: 2.2 MeV, 10 nA (3  C per sample) Si(Li) detectors Faraday cup aerosol sample PIXE SET-UPPESA SET-UP Results The comparison between the three samplers showed generally a very good agreement both for mass and for elemental concentrations. As regards the results from the analysis of the samples collected simultaneously in the three fractions, PM 2.5 and PM 1 turned out to be a substantial part of PM 10 ; excluding four days in which there was an anomalous increase in PM 10 concentrations respect to PM 2.5 and PM 1 (Saharan dust episode), the PM 2.5 /PM 10 and PM 1 /PM 10 ratios are (0.63 ± 0.09) and (0.46 ± 0.08) respectively. Al, Si, Ca, Fe, Sr and other typical crustal elements, and also Zr (produced by the manufacturing of tiles), are more concentrated in the PM 2.5–10 fraction, while elements like H, C, N, O, S, K, Zn, As (mean concentration 50 ng/m 3, with peaks up to 100 ng/m 3, related to emissions from artistic glass manufactures), and Pb are mainly present in the PM 2.5 and PM 1 fractions. C, N and O are the main aerosol components, with carbon giving the most important contribution to the total mass in all the fractions (about 40% in PM 10 and 50% in PM 2.5 and PM 1 ). Saharan dust episode Increase of the concentration of all soil-related elements (Al, Si, Fe, Ti) in the PM 10 fraction. Confirmed by back-trajectories calculations. Montelupo Fiorentino Sahara desert Back-trajectories by HYSPLIT (NOAA ARL) Picture from NASA PM 10, PM 2.5 and PM 1 mass concentrations during the simultaneous sampling of the three fractions. Percentage decomposition of the elemental concentrations in the three granulometric fractions. The values are averaged over the 3 weeks of simultaneous sampling of the three fractions.